Dithiolenes ethylenedithiolates

A number of complexes of copper with 1,1-dithiolenes are known they are interesting, inasmuch as they form (1) polynuclear species, e.g., [Cu4(i-mnt)3]2 . Recently, a copper(III) complex of 1,1-dicarboeth-oxy-2-ethylenedithiolate (DED ) was prepared (375) by oxidation of aqueous solutions of K2[Cu(DED)2] with a 10-15% excess of Cu(II) or H202, and of (BzPh3P)2[Cu(DED)2] with I2. The possibility of this system as a model for the Cu "/Cu. system in n-galactose oxidase has been pointed out. Lewis and Miller (113) also prepared M[Cu(S2C CHN02)2] (M = Cu, or Zn) and Cu[Cu S2C C(CN)2 2], and found that they are effective insecticides. 

Two main synthetic routes are available for the preparation of dithiolenes in the first and most frequently used method, either the free ethylenedithiol or an appropriate salt of the ethylene-dithiolato ligand dianion is reacted with a metal salt to produce anions of the dithiolenes, which may or may not be subsequently oxidized to the neutral species the second one, applied so far only to transition metal dithiolenes, converts vicinal diketones into dithiodiketones and reacts these either with zerovalent metals to form dithiolenes directly or uses metal salts to arrive at cationic species, which are reduced to the neutral dithiolenes either during the reaction or in a subsequent step. 

In the synthesis of the parent dithiolenes, the reaction of the disodium salt of ethylene-cts-dithiolate with metal salts is the only useful method.15 For the preparation of substituted dithiolenes the use of substituted ethylenedithiolates is the most efficient choice. In the synthesis of 1,2-dicyanoethylene-l,2-dithiolato ( mnt ) complexes, it is the only available method.16... 

Three main options, described in Scheme 2, exist for the conversion of dithiodiketones to dithiolenes (i) reaction with a transition metal carbonyl or other reactive zerovalent material (ii) reduction to an ethylenedithiolate and reaction as described above for these species and (iii) reaction with a metal salt to form a cationic dithiolene and reduction of the reaction product to the neutral compounds, whereby a suitable solvent (such as methanol) may serve the function of the reducing agent for in situ generation of the neutral species. 

Whereas complexes of ethylenedithiolate H2C2S212 are typically prepared by the reductive S-dealkylation of c -H2C2(SCH2Ph)2 (Section II.B), a viable alternative route involves base hydrolysis of l,3-dithiol-2-one, H2C2S2(CO).The parent H2C2S2CO can in turn be prepared on a multigram scale from chloroacetal-dehyde (82). This l,3-dithiol-2-one can be functionalized via deprotonation followed by C-alkylation (72), thus opening the way to a variety of functional dithiolenes (Eq. 7). 

Formigue and coworkers have successfully prepared asymmetrically substituted dithiolenes such as edt-CN (edt-CN = 2-cyano-l,2-ethylenedithiolate), tfadt and their square-planar nickel (49 and 50) and gold complexes . Both cis and trails isomers coexist and interconvert in solutions, while in the solid state the trails form is more commonly... 

The 0/1 couple in Au(tfd)21 (tfd = bis(trifluoromethyl)ethylenedithiolate, lb) occurs at a slightly lower potential (+1.32 V vs SCE in CH2CI2) than the mnt counterpart911. This is in accord with observations that in other transition metal 1,2-dithiolene complexes the ease of oxidation is dependent on X with X = Ph > CF3 > CN9. Replacing sulfur with the less electronegative atom, selenium, results in a lower oxidation potential for Aul lds)2 (tds = bis(trifluoromethyl)ethylenediselenolate, lc) relative to [Au( ltd) 12. More electronegative substituents make a complex easier to reduce, as expected. Thus, the 1/2 couple for Au(mnt)2 occurs approximately 500 mV more positive than the same couple for [Au(tds)2]. ... 

Ti etal dithienes (J), which are known also as dithiolenes (2), comprise a group of neutral complexes of metals with ligands derived from 1,2-dithiodiketones (l) or cis-l,2-ethylenedithiols (2). The complexes... 

To obtain ethylenedithiols, the main options described in Scheme 1 are available. Vicinal dithio-ethers, which can be prepared from cis-dichloro- or dibromo-alkenes or from alkenes through a stepwise synthesis, can be cleaved to produce dithiols (Route A). Ethylenedithiocarbonates can be prepared by several well-established procedures and by some less general ones as well. The ethylenedithiocarbonates are central intermediates for many dithiolene syntheses and for syntheses of derivatives of the electron donor tetrathiafulvalene (TTF), which has been intensively investigated in the past decade. This has widened the synthetic possibilities for ethylenedithio-carbonates. Their cleavage by alkali metal hydroxides or alkoxides produces salts of ethylenedithiolates (Route B). As an alternate route, their photolysis with loss of CO and generation of a dithioketone has been explored. ... 

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